In the container manufacturing industry, various approaches exist for fabricating and processing different container constructions, including bottles, cans and jars. For example, ram assemblies may be used to position and to shape a container that is being processed in a curling, cutting, expanding, necking, or other forming operation. Conventional ram assemblies comprise a cylindrical ram (piston), which moves axially relative to a turret shaft, and a plain bushing (housing), which is mounted to the turret shaft. The ram is moved, for example, by a turret barrel cam, in a reciprocating motion through the bushing. Historically, turret assemblies have operated by one ram assembly pushing a can, e.g., at a closed end of the can, into a forming head on a machine. A second, separate ram assembly then pushes a forming tool into or onto the can, e.g., at an open end of the can, to perform a forming operation.
Metal cans are often produced as “two piece” constructions, which consist of a cylindrical can body with an integral bottom wall and a can top. These cans are generally fabricated from thin aluminum or steel sheet metal. Aluminum cans, for example, are oftentimes used to package gas-pressurized liquids, such as beer and soda. For such applications, the can must exhibit a minimum predetermined strength so that it can withstand internal gas pressures generated by its contents, as well as the external forces from stacking, packaging and shipping, dispensing from machines, and handling of the can. However, the thickness of the sheet metal is a significant contributor to the overall cost of manufacturing such cans. If the thickness of the sheet metal can be reduced, while complying with strength requirements and other manufacturing tolerances, the cans can be produced at a decreased cost.
An example of a machine that forms the shape of the can body is known as a “necker” apparatus. Conventional neckers operate by applying mechanical pressure to the can body after it has been formed into its general body shape, e.g., a cylinder or multi-angular shape with an integral bottom wall. The necker is a type of tool-and-die apparatus in which the sheet metal is placed between a tool, having a protrusion, and a die, having a matching indentation. The tool and die are brought together, under pressure, forcing the sheet metal to assume the shape of the protrusion-indentation. A BELVAC™ (Belvac Product Machinery, Inc.) 595 Shaped Can Necker, for example, can form can bodies at speeds of up to approximately 2500 cans per minute. Can bodies are squeezed (“necked”) between opposite moving ram assemblies, namely a series of push rams which act as tools and an opposite series of knockout rams which act as dies. The can bodies, as they are progressed through the machine, are rapidly squeezed between a first pair of push and knockout rams, then a second pair of push and knockout rams, for as many as six or eight or more pairs of rams to complete the “necking” operation.
Each of the rams reciprocates back and forth at high speeds and with a relatively short travel distance of, for example, approximately 1-3 inches. Conventional necking rams are mechanically actuated, for example, by a “cam” mechanism, as air pressure actuators and electromechanical solenoid systems are oftentimes too fragile for the required high pressures and speeds and extreme shock loading. A cam is an elongated, raised rail with an oscillating (sinusoidal) track; each ram piston carries, at its rear end, wheels that fit on opposite sides of the cam track. As the cam track turns, it pulls and pushes the wheels of the ram causing the piston to move forward and backward. In addition to speed and travel, piston alignment is critical to ensure that the rams move with an exact timing and without binding. If a ram jams or becomes worn, it may fail and hold up the entire can production system. For that reason, rams are carefully lubricated, regularly inspected and, when necessary, replaced. Many modern machines use automatic lubrication, which typically involves running grease tubes to each ram assembly. For ram assemblies that are attached to a rotating turret, a special coupling for the grease supply line is necessary to distribute the grease to each ram. These couplings can wear out with time and use, allowing grease to escape. Even with proper lubrication, the rams may have to be inspected and replaced every few weeks, which is a large expense in terms of parts, machine down-time, time of skilled labor, and scrapped cans.
For some die neck progressions, the knockout (also known as a “knockout tool”) strokes thru the stationary die (also known as a “forming die”) to add support to the open end of a can during the reduction process. In addition to neck support, the knockout allows compressed air to enter the can to stabilize can position on a dome push plate, as well as to prevent the can from collapsing throughout the operation. A critical feature of a conventional ram assembly is an O-ring that is positioned on the outer diameter (OD) of the knockout. These O-rings aide in centering the knockout inside the stationary die to maintain consistent tool gaps, while allowing “float” for mobility with variations in incoming can wall thickness. The O-ring also helps to seal compressed air at the rear of the knockout, e.g., to prevent inadvertent venting, while maintaining maximum process support and minimizing utility requirements. O-rings also help to prevent grease, dirt and other contaminants common to neckers from entering the tooling thru the rear of the knockout proximate the tooling ram (also known as a “drive cylinder”). O-rings are typically staged in a dynamic setup with high-speed reciprocating motion and limited cross-sectional squeeze. In addition, the only lubrication an O-ring will typically see is residual mineral oil or wax used on the can for necking. As such, O-ring operational life expectancy is minimal and, thus, must be replaced on a regular basis to maintain function. This increases parts and labor costs which, in turn, increase overall manufacturing costs.